Short electromagnetic horn particularly for long wavelengths



Aug. 29, 1961 B. G. HAGAMAN 2,

SHORT ELECTROMAGNETIC HORN PARTICULARLY FOR LONG WAVELENGTHS Filed Aug. 24, 1959 INVENTOR 30 v/v ra/v //44M4N M7, fm ATTO R N EYS United States Patent 2,998,603 SHORT ELECTROMAGNETIC HORN PARTICU- LARLY FOR LONG WAVELENGTHS Boynton G. Hagaman, Falls Church, Va., assignor to Antenna Systems, Inc., Washington, D.C., a corporation of Delaware Filed Aug. 24, 1959, Ser. No. 835,665 9 Claims. (Cl. 343-781) The present invention relates to electromagnetic horn antennas and particularly a method and arrangement for shortening the length of such an antenna.

In my prior Patent 2,851,686, I have disclosed tapered aperture horn antennas having reduced side lobe radiation. Such antennas are useful for directionally transmitting or receiving not only very high frequency waves, but also radio waves of rather long wavelengths, for example waves having frequencies down to two or three megacycles. These horn antennas must, of course, have large dimensions. The horn aperture may have a width and a height of several hundred feet and the length of the horn is even greater. It is, therefore, very desirable to reduce the length of the horn, but generally this cannot be done without impairing the directivity of the radiation pattern. It is a principal object of the present invention to shorten the length of an electromagnetic horn without impairing its operation.

According to my invention, a horn antenna, which may take various shapes some of which are illustrated in my Patent 2,851,686, is cut 01f or truncated at a distance from its aperture which is much less than its normal length, for example somewhere near its normal midpoint. In the cut-ofl plane, the horn is closed by a reflecting back wall or surface. Positioned in front of the aperture of the antenna is an exciting source or a feed antenna. The feed antenna may be a section of wave guide provided with a small horn antenna such as a flared rectangular horn. A feed horn having a tapered aperture can be used, but is not necessary inasmuch as the characteristics of the composite antenna have the side lobe suppression and the other advantages afforded by the tapered aperture of the main horn. Preferably, the feed horn is placed so that it offers minimum interference with the radiated beam of the main horn. For this purpose, the feed horn may be placed below the axis of the main horn and tilted upwardly so as to radiate toward the main horn. The horn antenna according to the invention operates as a true horn and has hornlike propagation therewithin and not merely reflection from a shaped reflector.

The invention will be fully understood from the following description and the drawings in which the figure is a perspective view of one embodiment of my invention.

Referring to the drawing, there is shown a tapered horn antenna of the pentagonal type analogous to that shown in FIG. 6 of my above-mentioned patent. The horn 10 may actually have various shapes known in the art, and particularly the several shapes shown in my above-mentioned patent. But for the sake of simplicity of illustration of the invention, the pentagonal form only is shown herein. The horn 10 includes five side walls 11-15. Walls 11-15 define an aperture 16, particularly adapted to radiate waves which are horizontally polarized. Walls '1115 taper from the aperture 16 to a back reflecting wall 18. The wall 18 closes and terminates the horn 10. Normally, horn 10, it formed as shown in FIG. 6 of my patent, for example, might have a length about twice as great as in the present instance. It will be noted that the vertical width of the aperture, hich is the ection normal to the eletcric vector,

Patented Aug. 29, 1961 ice varies from a maximum value at the center of the aperture to a minimum value at the two ends of the aperture.

The exciting means for the aperture is preferably a wave guide radiator 20 which may consist of a small horn antenna 22 connected to a rectangular wave guide 24 provided with suitable feedor transmission means 26 for energizing the horn antenna 20. The horn 22 i. adapted to radiate 'a horizontally polarized electromagnetic field through the aperture 15 into the main horn 1'0. Antenna 20 is preferably partially removed from the path of the aperture 16 or horn 10 by depressing or lowering antenna 20 and tilting it upwardly. The horn 22 may be a flared rectangular horn, although it will be understood that other types of horns including the tapered aperture type illustrated in my Patent 2,851,686 could be used as feed horns.

By the use of the relatively small and short horn antenna 20, the normally very large main horn 10 can be greatly reduced in size and thus afford a very great saving in expense both of construction and required land area for the antenna. The energy fed to the main horn by the feed horn is reflected from the back wall 18 toward the aperture 16 producing the side lobe suppression and the other advantages of a large tapered aperture horn antenna.

Although for simplicity I have explained my invention with reference to a single embodiment thereof, it will be understood by those skilled in the art that the antenna disclosed herein may be used for reception as well as transmission and that the principles of the invention are applicable to various other arrangements, and particularly to horns of diflerent shapes, within the spirit and scope of the following claims.

I claim:

1. An antenna comprising a main truncated pyramidal electromagnetic horn having a radiating aperture, the small end of said horn opposite the aperture being closed by a back reflecting wall, said main horn having such a short length that its closed end has dimensions equal to a major fraction of the corresponding dimensions of the aperture, a feed horn positioned in front of said aperture, said feed horn having its radiating aperture facing the main horn aperture, and wave transmission means connected to the feed horn, whereby said main horn is irradiated by said feed horn.

2. An antenna comprising a main truncated flared electromagnetic horn having a radiating aperture and plane side walls, at least two of said side walls being inclined toward each other and the distance between the inclined walls in the direction perpendicular to the electric vector decreasing from the center to the ends of the aperture, the small end of said horn opposite the aperture being closed by a back reflecting wall, said main horn having such a short length that its closed end has dimensions equal to a major fraction of the corresponding dimensions of the aperture, a feed horn positioned near said aperture, said feed horn having its radiating aperture facing the back wall of the main horn and its radiation beam axis inclined to the axis of the main horn, and wave transmission means connected to the feed horn, whereby said main horn is irradiated by said feed born.

3. An antenna according to claim 2 wherein the walls of the main horn are arranged to form a pentagonal aperture.

4. An antenna according to claim 3 wherein said walls are arranged so that one side of the main horn aperture is substantially parallel to the earths surface and the horn is symmetrical about a vertical plane.

5. An antenna comprising a main electromagnetic horn having a radiating aperture, said horn having a plura itv of plans aids a plurality o sa d s de walk being inclined toward each other so that the distance between the inclined walls in the direction perpendicular to the electric vector decreases at the ends of the aperture, the end of said horn opposite the aperture being closed by a back reflecting wall, said main horn having such a short length that its closed end has dimensions equal to a major fraction of the corresponding dimensions of the aperture, and means positioned in front of said aperture for radiating substantially plane polarized electromagnetic waves through said aperture into said horn.

6. An antenna according to claim 5 wherein the walls of the main horn are arranged to form a pentagonal aperture.

7. An antenna according to claim 5 wherein said Walls are arranged so that one side of the main horn aperture is substantially parallel to the earths surface and the horn is symmetrical about a vertical plane.

8. A shortened electromagnetic horn antennafor waves having frequencies below fifty megacycles, comprising a main flared horn having a radiating aperture, said horn having a plurality of plane side walls, inclined toward each other so that the distance between the inclined walls in the direction perpendicular to the electric vector decreases at the ends of the aperture, the small end of said horn opposite the aperture being closed by a back reflecting wall, and means positioned in front of said aperture including a plane polarized wave directional antenna.

9. An antenna according to claim 8 wherein said plane polarized wave antenna includes a flared rectangular feed horn positioned in front of said aperture, said feed horn having its radiating aperture facing the main horn aperture, and wave transmission means including a rectangular wave guide connected to the small end of the feed 

